Bar gripper means for stretching presses



May 13, 1952 1'. B. HAwKEs 2,596,772

BAR GRIPPER MEANS FOR STRETCl-IING PRESSES Filed April 25, 1946 y 2 SHEETS-SHEET 1 45 TJCE..

INVENTOR: 7.' 5l MWA/ss. i BYWywmv/mg l, g MMM ATTORN 5.

May 13 1952 T. B. HAwKEs 2,596,772

BAR GRIPPER MEANS FOR STRETCHING PRESSES Filed April 25, 1946 2 SHEETS- SHEET 2 INVENTGR: 2' 5. /654/4//4/55.

BY WMM, Kwwu'ilj Patented May 13, 1952 BAR GRIPPER MEANS FOR STRETCHING PRESSES Thomas Blair Hawkes, Champlain, AN. Y., assignor of one-half to. The Sheridan Iron Works and one-half to T'. W. & C. B. Sheridan Company, corporations of New York AppiicationAprrii 25, 1946, serial No. 664,925

. e sclaims. (c1. ,2i-*243) l 'Ihis invention relates to the subject of stretching of bars, especially metal bars; withspecial reference to a gripper means or device adapted to grip and hold each end of the barv to be stretched, for example in a power apparatus Vor press for effecting stretch-shaping ofV such Workpieces or bars, that is, the curving of the `same about a suitable die or form while applying stretching pull to the work.

This application is a continuation in part of.

the present application of Hawkes, Serial No. 473,943, filed January 29, 1943, now Patent No. 2,431,173 for the Stretch-Shaping of Bars, Sheets and the Like; and containing additional matters of disclosure. Said Patent No. 2,431,173 granted November 18, 1947 thereon may be referred to for 'ascertaining various general features of structure and operation not hereinfully disclosed, and as well detail-s of arrangement, construction and mode of action not requisite herein for a disclosure of the subject matter of this invention.

A general object of the present invention is to aiord a construction of gripper, or bar` gripping device, of high eciency and reliability for the holding of one end, or preferably bothends, of the workpiece or bar .to be stretch-shaped or otherwise stretched. A further object is to alord such a gripper device which'is simple and rugged in structure, smooth inaction, and gives a powerful gripping and secure holding of each bar end during the stretching operations. Another object is to afford such a gripper device which, notwithstanding its bodily displacements during stretching actions, is readily maintained in connection with power means through which the closing of the gripper upon the work is brought about and maintained until the final release. More especially the invention has for a particular object the alfording of effective hydraulic operation of the closing and opening of a work-bar gripper for the purposes of the recited stretching operations thereon. Further objects andradvantages of the invention will be explained in the following description of illustrative embodiments thereof; and to the attainment of such objects and `advantages the invention consists in the novel gripper device and the novel features of combination, arrangement, construction and detail herein illustrated or described.

In the accompanying drawings, Fig. 1 is a more or less diagrammatic front elevational view of a stretching, or stretch-shaping, machine or press, and containing gripper devices embodying the present invention.

Fig. 2 is a top side view partlyin central sec- 2 tion of an effective hydraulically operable gripper device, such as that indicated in Fig. 1, embodying `the principles of the present invention.

Fig. 3 is a complete sectional view of the grip-V per device taken centrally at right angles to Fig.

2, in its position before the bar has been gripped. Fig. 4, in sectional view similar to Fig. 3, shows the central or gripping portion on an enlarged scale and with the gripping parts in gripping position.

Fig. 5 is a detached left elevational view of the interior side of the interchangeable cover wall or plate, upon a reduced scale.

Fig. 6, in central longitudinal vertical section, show-sa modified form of gripper device embodying the same basic principles as disclosed in Figs. 1 to 5, and illustratively designed for the stretching of I-beams. Fig. 7 is a transverse vertical sectional view taken on the section line 1 1 of Fig. 6. In Figs. 6 and 7 the pressure is slack and the bar not gripped. Fig. 8 is like Fig. 7, but under gripping pressure. Fig. 9 shows in detached perspective the rubbery mass of Figs. 6 to 8 in an annular form with shaped central recess; While Fig. 1,0 is similar but showing a circular recess.

Fig. 11 shows in end elevation an illustrative form of I-beam adapted to be gripped by the device of Figs..6 to 13 `or that of Figs. 14 to 16. Fig. 12 is a lefthand elevation of the removable cover plate of the gripper device of Fig. 6 or 14.

Fig. 13 is a detail view in sectional perspective showing the construction of an illustrative ilexible, expansible pressure chamber as embodied in Figs. 6, 7 and others.

Fig. 14 is a central longitudinal sectional view like that of Fig. 6 but showing another modification constituting a third embodiment of the invention. Fig. 15 is a transverse sectional view like that of Fig. 7 taken on the section line I5l 5 of Fig. 14. Fig. 16 is an enlarged view of the structure of the rubbery mass of Figs. 14 and 15.

In Figs. 1 to 5 the workpiece or bar, as a convenient example,\is considered as a T-bar, with single flange and single central web, as shown; while in Figs. 6 to 15 the bar is considered as an I-bar or beam, `constituting another example, with web and two flanges, although naturally many varieties of extruded or similar bar shapes may be gripped 'and stretched by the use of bar gripper devices constructed on the principles of the present invention.

The general parts of the press or stretching machine require but little description, constitut- 3 ing an illustrative use of the gripper device hereof.

The blank or workpiece B may be a bar of an extruded or other shape; and for example it may have a web portion B' and a flange B2, combined as a T-bar, or it may have two such iianges rendering it an I-bar; or it may be an angle bar, a channel, or other shape. Fig. 1 shows' a T-bar B being operated upon, and in this embodiment, following the parent case, the stretching is coordinated with bending or shaping, by means of a die D, in the nature of a curved pattern, adapted to bev lifted to cause curvature of the blank while being stretched around the die. tend die rams 21, in the nature of plungers, carrying at their top ends av saddle or rising support 2e upon which interchangeable dies D may -be mounted; there being shown pivots 29 between the rams and saddle in `case rocking movements of the die are desired. The rams 21 are mounted for vertical sliding within cylinders 30, operable hydraulically `from below. For stretching Without curving of bars the die andoperating means may be allowed to remain idle, or wholly omitted.

Upon Athe general base are suitably mounted an opposite pair of carriages for the' gripper Vmechanism,l there being shown a. lefthand carriage 3l and a righthand carriage 32, which may be slidably rectractible upon the base and each carrying the mountings for one' of the two grippers G, G.

One of the gripper mounting means comprises a tiltable head 45, trunnioned upon each ofthe carriages 3| and 32; and each head1 is shown as a hydraulic cylinder containing a piston operable through its rod 'I5 to retract and return the gripper, pipes and lc being indicated for supplying pressure liquid to and-from the opposite ends of the cylinder 45 to effect such operations. Suitable means 49, including a rack, may be embodied to tilt the head 45 upwardly and downwardly when the bar is to be curved, and other means 64 including a turretl may be embodied to rock the gripper when desired about its axis of longitudinal movement onth'e carriage.

The gripper G illustratedin Figs..2 to 5 has a stem Vl5 which preferably also is the piston rod or `connector part by which the gripper is mounted upon the head or hydraulic cylinder 45. ',Ifhe gripper is hollow, having an outer box or housing 16 containing ample space for the interior gripping and operating elements. The bar B intrudes axially Within the housing or'box and is surrounded by rubbery or resiliently flowable gripping means -operated by surrounding meansfarranged to cause inward pressure to deform the rubbery elements or blocks and distribute the resulting pressure directly or indirectly to the bar. In this embodiment .the surrounding means comprises a plurality of xed hydraulic instruments or cylinders 11 and contained movable elements; two of such cylinders being illustratively shown, radially arranged around the housing and able to develope and apply the inward thrusting forces to deform the intermediate mass of plastic material or rubber and thereby apply holding grip to the intruding bar end, as will be more fully described.

The gripper G has its box or' enclosure T6 surrounding its gripper chamber.Y The box proximal wall 18, that i's, nearest the center of Above the general base exthe press, facing the die D, has an open aperture 'I9 to receive with snug Vrit the end of the bar to be gripped and stretched, its distal wall being united with the gripper stem l5, these parts and the box side walls 8| being shown in Figs. 1 to 5. Preferably the proximal housing wall 'i8 isremovable, by releasing its attaching bolts, and interchangeable for others with openings '19 to receive bars of other shapes; being thus adetachable cover wall or plate.

The gripping means within box T6 and adjacent thereto comprises resilient opposite squeeze members or rubbery blocks acting upon the workpiece or bar, preferably through interposed rigid jaw members 83; and there is shown' means in the form of rigid plungers 86 to compress theV squeeze members when operated by pistons working in cylinders under hydraulic actuation as will be described. The parts are shown relaxed and the gripper released in Figs. 2' and 3 but are gripping the work, a T- bar', in Fig. 4.

In the use of the gripper so described the blank orv bar B to be shaped is manually inserted endwise through the aperture 'I9 and its end thus extended into and acrossthe interior of the lgripper box, where it is gripped and held. ItI is preferable insome cases to provide rigid jaw blocks, such as blocks 83, between which certain portions such as the web of the blank may be directly gripped, these blocks being of sectional shape to occupy and fill out the section of the blank thereby eliminating deep recesses and affording' for example a quadrangle. The block inserts 83v may be surfaced or cross-scored like a le to give a stronger grip on the bar.

To avoid having the jaw blocks 83. initially loose in the box, or attached toV the. rubbery squeeze blocks, they are preferably suitably mounted in a, position to be ready for the gripping action, and for convenience this is herein done by attaching or forming said jaw blocks upon the inner side of the apertured wall or plate 13,V as seen in Fig. 5, and. the mounting may be either loose or fast, in thel latter case the two blocks being capable of `deflection for the gripping. action. When these parts are so assembled and the blank inserted, the blank is subject to the gripping pressure of the roughened jaw blocks 83 bearing on .the blank web, while the outer sides of the bar flanges are exposed, as are the edges of its web and flanges,A these parts thus being in readiness to receive high .clamping pressure adapted to prevent' the bar slipping out of its gripped position.

The Vactive gripping element of the disclosed gripper consists of the rubbery or similarly yieldable squeeze blocks 85, surrounding the work piece andsurrounded by the pressure producing means which deforms the rubbery mass to cause gripping pressure. These yieldable or owable rubber'blocks are located with the jaw blocks and blank centrally inside or between them, and are composed preferably or" plastic rubber or the like, so that normally they retain their shape as seen inY Fig'. S'until deformed for gripping purposes. Initially, when the blank is rst inserted, there may be empty spaces at both lateral sides of the bar and jaw blocks, as shown; or the squeeze blocks might be initially shaped to occupy partly or wholly such spaces, as disclosed in Figs. 7 and 15. y

Beyond or surrounding the opposite rubbery squeeze means or blocks Y85 are shown in Figs. 2 to 4 a pair' of rigid or metal pressure blocks 86,

having a Vtight sliding t in the otherwise open top and bottom of the gripper box, thereby to act as compression plungers giving inwardthrust upon the squeeze members 85. The walls of the opposite hydraulic cylinders 11 extend inwardly toward the gripper box walls, with cutaway extensions 81 between which-the opposite compressing blocks 86,- 86 may slide toward and from each other. Beyond each of theV two plunger blocks; Aand occupying the full section of each cylinder 11, is a piston 89 working therein and adaptedito thrustV the adjacent pressure block toward the Vcenteror gripping position of the device. For preventing leakage of hydraulic liquid,the outer end of each piston is shown provided with a packing cup 99 upon which bears a washer 9| attached' by screw 92 to the piston.

The described assembly of a plurality of surrounding cylinders, with gripper box and-chamber between them, Vand various interior parts, is completed as a unitary device by the provision ofv endpieces or head walls 93 into which the outer ends of the respective cylinders are set, and which lend walls 93v have extensions or lugs to receivei longitudinal tie-bolts 94 adapted to unify rigidly the entire gripper'device. V'I'he various xedparts or walls may be' suitably held together as by means of the clamping pressure of the end pieces, although the perforated wall 18 is preferably removable as stated.

The gripper device is completed by the provision of power thrusting or piston operating means. There is shown a liquid lchamber 95'ibetween each pistonV and the adjacent end wall 93, with an entrance passage or pressure port 96 through such wall, having a nipple connection 91 to a supply pipe 98, these being lled with hydraulic liquid L supplied from any suitable pump or source of pressure, with valve control. Preferably the two pipes 98 are interconnected with each other and with a common pressure source, as shown for `example in Fig. 3, so that an equalizing pressure action lconverging upon the blank is produced. Thus, the pistons and the vparts between them may be caused to deliver a high mechanical pressure upon the workpiece, the rubbery blocks 85 grippingv the bar in partr directly and in part through the jaws 83. Fig. 4 shows how the rubbery masses 85 are Vcaused to flow and become molded about the workbar and jaw blocks under their heavy compression, giving intense and rm friction rhold upon the bar, adapted to fulll the purposes described. In order to permit the various necessary movements of the gripper during operation the liquid supplying pipe 98 should be a flexible lconnection or hose, such as a thick-walled rubber tube; and the control of the described hydraulic and gripping actions may be manual or under automatic timing.

The use of a plurality of the radial cylinders containing pressure means affords more complete distribution of pressure upon the rubbery mass 85, which transmits it to the bar. While the mass is shown in two sections and could be in many pieces stuffed into the gripping chamber, it is in effect an annular mass, in its embracing or enclosing of the bar, and becomes a quadrilateral annulus when under deformation as in Fig. 4. The spaces 95 constitute a pressure means or plural chamber, each one having its inwardly yielding wall or piston 89 to thrust through plunger 86 upon the plastic mass, the'outer and lateral walls being stationary.

A'The barv gripper hereinabove described and Iii) shown in Figs. 1 to 5 may be summarized as follows as to its principles of structure and operation, which principles are embodied also .in the alternative grippers of the-remaining gures of the drawings. The gripper as a whole has a walled enclosure, which may be considered. as a closed box, containing a substantial hollow Aspace serving as a gripping chamberl and accommodating the end of the bar, that is, a short length thereof, and a bar gripping means. The proximal wall of the enclosure, being the wall nearest to the `middle portion of -the bar, is apertured for the clcse-tting longitudinal sliding entry of the barV into a lcentral gripping position within the gripping chamber. The interior gripping means comprises a mass of rubbery or other` suitable elastic material disposed within the gripping chamber in a manner to embrace or to surround thebar position, and deformable under the stress of pressure to exert a gripping thrust, direct or indirect, uponv the bar. In combination with said embracing mass is a pressure means. disposed outwards of the mass and movable centripetally to apply an inwardly directed forcible deforming pressure to the mass. By this arrangement, when the pressure means is operated it causes the rubbery mass to be deformed to exert centripetal thrust upon the bar end to grip and hold it against longitudinal displacement until released.

The embodiment of Figs. 6 to 13 operates upon the principles thus described, and certain of the parts correspond approximately with certain of those already described. Instead of the stem 75 of the first form of the invention, the second form has a mounting lug or ear .15A formed or 'attached upon the gripper box or housing 16A. At its proximal side the housing is closed by an apertured inner wall or cover plate 18A, readily detachable and interchangeable by removing the eight bolts which hold it in place.

The bar B, being an I-beam, has its web B' and flanges B2,B2, and to accommodate snugly the entry of such a bar the cover plate 18A is formed with the opening 19A, of the same I-shape, with suiicient clearance to permit the sliding entry of the bar to its central position within the main or gripping chamber of the box. The" distal or outer box wall 89A carries the mounting lug 15A. In this embodiment the enclosure or housing is completed by the cylindrical wall BIA, preferably integral with the wall A and receiving the attaching bolts of the removable cover wall.

When the bar or blank is of a shape with deep recesses rendering it difficult for the rubbery mass to ow therein and contact all parts of the bar, as is sometimes the case with an I-beam, it may be desirable to supplement the bar by applying rigid blocks, such as steel jaws 83A at suitable points to afford substantial convexity for the gripping engagement. Thus Fig. 7 shows these blocks, of roughened steel, lling the concave spaces within the bar outline; and they may be supplemented with analogous blocks 84A locatedA against the bar-flanges. This feature however is optional, since the jaw blocks need not always be interposed, and the gripping contact of the rubbery mass may be directly upon all parts of the bar, as seen in Figs. 14 and 15.

In these second and third embodiments the rubbery or elastic material is shown in the form of av substantially annular mass 85A, which thus not merely embraces the workpiece but surrounds it, for gripping action upon all exposed 7 sides thereof, stress'.

For producing the centripetal stress upon they rubbery mass a pressure means-is provided, disposed outwards of thepmass and movable in-V wardly to create the deform-ing and gripping pressure. Instead of the movable rigid plungers 86 of the rst form', operated from the exterior,

thesecond embodiment employs ahydraulic pressure chamber 95A, inthe nature of a hollow diaphragm, composed of flexible material, with its Ainner side bearing againstthe annular rubbery mass and its outer side: backed upby the cylinder wall SIA, the chamber being of the form. of a substantially complete circle, that is, annular, sov as to bear inwardly and convergingly toward the general axis or center around the entire periphery of the rubbery mass.V To cause the flexible pressure chamber to expand inwardly its outer side is formed with .an opening in alinement with. a passage or port 96A extending through. the .cylindrical Wall to an exterior point, whereat itI carries a threaded nipple 91 coupled with a-iiexibletube or hose 98 leading from any valved source of hydraulic pressure. The tube 98, port 96A and chamber 95A are filled with an oil` or other suitable hydraulic liquidL, and when pressure from the source is applied, the swelling of the pressure chamber causes the eentripetal thrust ofV the rubbery mass either directly upon the bar to be gripped or upon the metallic gripper blocks or jaws 83A which in turn press upon. and hold the bar against displacement. The pressure means or chamber 95A, being a normally collapsed but inflatable annular bag or tube of rubber, fabric or the like, delivers an equalized inward pressure around allsides of the bar. Y

The flexible pressure chamber may act somewhat as a bellows, expanding with the introductionof. the hydraulic ii-uid, and'for the following reasons its actual expansion movement. need not be excessive. In Figs. 6 and '7 the pressure chamber 95A. is shown .as being slack or deiiated, so that the rubbery mass is in its normal position, and. the bar B can enter loosely. In this embodiment the central recess in the rubber mass is preshapedso as to conform substantial.- ly with the outline of the metal parts to be acted upon, in this case the bar B with the steel `iaws appliedthereto. By reason of this arrangement a quite small pressure movement alfords the necessary grip. Fig. 8 differs from Fig, 7 in that the pressure .chamber or bellows is expanded inwardl-y,` the rubbery mass being thus contracted and gripping the central parts. The detached view in Fig. 9. shows the rubber mass ybefore in-Y sertion into the gripper, indicating its shaped central recess 99 `corresponding with Fig. 7. By having a sufficiently greater degree of expansion of the pressure chamber the rubber mass may be in the form of a true circular annulus vfor example as shown in Fig. 1 0, with Iround recess 10U.

vA simple manner of constructing the pressure chamber 95A is ill-ustratively shown, consisting in 'the preparing of complementary chamber wall portions 1.48, each of U--shape as more `clearly shown in Fig. 13. Each of the wall members may consist of a flexible Ypacking material, of well when placed under deformingV pressure'. .chamber or ibagmayl be formed many-f concavity or. gutter against which .one end. of.

the pressure chamber rests, whileat the other end, in contact with the removable coverwall 18A is a complementary guttered ring [52. The. outer side. of. the iiexible chamber lbears' against the gripper chamber cylindrical wall 81A, wl'u'le the inner side of the pressure chamber bears against the rubberyA mass` A. When the vhydraulic: pressure is applied to they pressure chamber it expands inwardly, forcibly contacting the rubbery mass .at the .periphery .0f the latter thereby causing the inner portion of -the mass to exert gripping pressure upon the workpiece as already described, around` its periphery.

The third 'embodiment `of the invention, shown' in Figs. 14 and 115, dilers mainly in twoJrespects from the second embodiment. In the first place. the supplementalholding jaws 83A, 84A are omitted, therubbery mass 85B being arranged to make direct Contact with the bar to be stretched. the second place, the rubbery mass is of a special advantageous form, the rubbery or plastic matcrial having embedded in it, and substantially iilling it, a multiplicity of small shot or steel balls I ,54, which may be in contact with each other within the mass but due to the elastic nature of the mass are .capable .of relative movement, while locked in the embedding material. This structure has advantages in stabilizing` the annular rubberymass, and more particularly it provides, .at the inner or gripping vsurface thereof, a highly efficient gripping surface, whereat' the exposed balls may contact substantially directly against the surface of the 'bar to be held, with the rubbery matrix material also contacting V`the bar between the contact p oints of the balls. Such an elastic gripping mass is found to be. adequately deformable for the purpose and to provide a high degree of holding action preventing longitudinal displacement of thebar within the gripper. See Fig. 16.

When the metal grip pieces 83A Vor 84A are used they kpress directly upon and hold the bar, the rubbery mass applying the pressure; in that casethe rubber need not flow into deep recesses. The rubber mass, whether or not shot-filled, could be preformed or cut for its recess to t loosely the bar and the adjacent grip pieces, or the bar alone, as shown. A satisfactory way to preconstruct such a mass is as follows. A dummy chamberor mold is formed corresponding to the gripper chamber in size and shape. It is set with its open side upward and a dummy piece, insert or core corresponding to the bar, with or without the grip blocks, is correctly positioned therein and held by a clip, bracket or'otherwise. The vulcanizable rubber material is placed in the mold to the proper depth, preferably precededby the steel shot .when used. The mold is closed and pressure and heat applied in any Way known to the rubber art, causing the ,embedding .of the shot, and then, in due time, the molded mass ibecomes cured or vulcanized into the resilient product or annular mass desired. In the case of other elastic plastics e. g. thermosettable material heat is lapplied to the molded mass in accordance with approved practice. The dummy insert or core is preferably slightly larger than the rdesired shaped recess soas to provide clearance for insertion of each bar into gripping position. When the recess is to be substantially larger, for example as in Fig. 10, to accommodate various bar shapes, a circular core is used in the mold. When removed from the mold the mass can be positioned within the gripper chamber and the ring |52 and cover 18A applied, completing the gripper for gripping and stretching purposes.

Anyapproved way to mold and vulcanize the rubberymasses 85 or 85A or 85B can be used. Moldable crude rubber may be used, softening and ilowing to embed the shot during the heating under pressure when curing. Or the plastic material and shot could be premixed, before molding.

The annular chamber 95A can be variously constructed; the use of two separate annular U-packing strips being convenient. The inner and outer lips of each part press respectively against the rubbery mass 84A or 84B and the chamber peripheral wall 8|A, and these contacts tighten with increase of pressure, suiiciently to prevent impairing leakage. The opposed inner lips could be cemented to the rubbery mass to improve the fit at this point. For building up the annular chamber out of two rings of packing a recently introduced form of packing strip is` `hydraulic medium is forcibly introduced.

The disclosures of Figs. 6 to l5 may be summed up as follows. In these forms the gripper device has a walled housing or enclosure 16A with peripheral and end walls and containing an annular gripping chamber one end wall of which is apertured for the longitudinal entry of the' bar end into its axial gripping position within the chamber. The interior gripping means comprises a ring or annular mass 85A of rubbery material disposed to embrace surroundingly the bar position and deformable under pressure to` exert gripping thrust upon the bar, with a pressure means surrounding said ring or annulus and operable centripetally to apply an inwardly directed forcible deforming pressure to the ring. Thereby when said pressure means is operated the rubbery ring is caused to exert centripetal thrust upon the bar to grip and hold it against longitudinal displacement in the gripper. Preferably the pressure means is annular, extending around the entire circumference and operative to constrict the rubbery gripping ring; and is shown as a hydraulic chamber 95A, confined outwardly and longitudinally by the housing walls, thus necessarily expanding inwardly when hydraulic pressure is admitted, after the bar is in axial position, thus causing equalized centripetal pressure around the entire gripping ring and complete gripping and holding by the constricted ring of the bar end.

What is claimed is:

l0 1. For a bar stretching machine a gripper device comprising a gripping annulus composed of a matrix of rubbery material elastically deformable inwardly for substantially direct gripping action upon the bar; and embedded in said matrix numerous hard 'shot relatively movable with the deforming play of the matrix material and providing at the gripping surface an effective gripping action. preventing relative sliding of the bar with respect to the gripper device.

2. For a bar stretching machine a gripper device comprising peripheral and end walls enclosing a central gripping chamber containing an annulus composed of a rubbery mass' providing a matrix elastically deformable inwardly for gripping action on the bar end, said end wall having a hole for close-fitting entry of the bar end centrally into the chamber; and means disposed outwards of the rubbery mass for applying inward pressure to deform the mass and cause it to grip the bar for holding it against displacement; said rubbery mass having embedded in it numerous small hard separate particles relatively movable with the deforming play of the matrix material and adapted to provide an eiective gripping action between the gripper device and the bar end.

3. For a bar stretching machine a gripper device comprising peripheral and end walls enclosing a central gripping chamber containing a generally annular rubbery mass providing an elastically deformable bar end gripping action, and said end wall having a hole for close-fitting entry of the bar end centrally into the chamber; and means disposed outwards of the rubbery mass for applying inward constricting pressure to deform the mass and cause it to press upon and grip the bar end for holding it against displacement; said rubbery mass having embedded in it a multiplicity of small hard shot-like metallic bodies relatively movable within the rubbery mass and adapted to provide an eifective gripping action between the gripper device and the bar end; some of which multiplicity of hard bodies lying at the surface of the rubbery mass and exposed to substantial contact against the bar end thereby to impress the bar and enhance the gripping effect thereon.

4. For a machine for stretching metal bars, a bar gripper device having a walled enclosure formed with a central gripping chamber accommodating an enclosed means for gripping the end of the bar inserted therein, the proximal wall of the enclosure having an entrance hole for the close-fitting longitudinal sliding entry of the bar end into a centrally projecting position within the gripping chamber the enclosed bar gripping means comprising 'a-r'nass of rubbery material disposed to embrace'surround'ingly the centralportion of the gripping chamber and deformable under exterior pressure to exert gripping thrust by the rubbery mass upon the bar, and means for applying pressure disposed outwards of said mass and movable in the chamber to apply an inwardly directed forcible deforming pressure to the mass; so that when said pressure means is operated the rubbery mass is deformed to exert inward thrust upon the bar thereby to grip and hold it firmly against longitudinal sliding displacement in the gripper device; the rubbery mass being impregnated with a multiplicity of small hard shot including numerous ones exposed to substantial contact against the bar whereby the pressure acts through such shot to impress the bar and make rigid the connection between the gripper device and the bar.

5. A bar gripper device as in claim" 4 and where- 'to surroundand grip vvthe centrally projecting end of -tlie bartobe Istretched in `artight manner to prevent relative movement between the :walledrenclosure and the bar end. Y

.6. For useina metal .ibarstretchingf'macliina a bar gripper device having Ya walled housing with Vperipheraland endwalls Aand containing va gripping chamber accommodating an enclosed means Afor gripping Vthe :lateral sides .of the fend portion .of va bar .,slidingly inserted 'through an' end 'Wallinto its axial gripping position Within thegripping chamber; the enclosed bar gripping means comprising `an annulus of rubbery material disposed to embrace surroundingly the'positionrto be'occupied by the barend and deformable under pressure -to Vexert inward gripping thrust upon .the bar end, pressure means surrounding said'annulusandrconsisting of a circumferential pressure vchamber which is expansible inwardly but otherwise confined, and the walled :housing having aninlet' passage leading into* said pressure chamber for conducting liquid vfrom v-a pressure source tothe pressure chamber; whereby when saidpressure'means is operated-the rubbery annulus is deformed arounditszperiphery and thus caused to' exert equalized centripetalthrust upon the bar causing the latter to' grip and 'hold ythe bar againstsliding displacement in the gripper; the said rubbery'annulus havingembedded therein a largenumber of hard-metal shot of vwhich many are exposed "to fsubstantial'contact at the annulus surface whereby whenfgrippingj'pressure is applied to the rubbery mass it actsthrough-the surface `shot 11o-enhance the `eiectiveness `of vthe bar gripping action.

7. .For a machine vfor stretching -meta1-barsfa bar gripper .device having :a walled enclosure formed with vcentral gripping vchamber accommodating anY enclosed means for. grippingthe end Aof the `bar inserted therein, the proximal wall ygrip-and hold it rmlyagainstsliding displacement in the ygripper -device; land Asaid I'elastically kcompress'ible material `being in the form v"cf a shapedimass whichlhas embedded, atleast in 'the contact surfaces fthereof, numerous fsmall'hard shotzadapted to make contact Awith ithebar-fend whereby the pressure acts lthrough the i'naterial and thefshot Ito afford frigid gripping 'of -thebar Vend ,within the enclosure .of the r gripper i device.

.8. For ametal' bar-stretching or shaping machine, a1 barfgri'pper :device lhaving'awalledhousing',` containing aY gripping chamber :accommodating vaan l'enclosed means .for receiving Y through la fhole in an 'end=wall, and for gripping'thelateral sides 'of the endportion Vof the bar 1in aniaxial gripping position vwithin the rgrippingfchamber; the enclosed bar gripping 4means comprising an vannular mass or'ring of;rubbery material-disposed -to wembrace `surroundingly @the fcentral portinn of the-chamber, andsaidgripping:meansbeingrdefurmablezunder pressure -toexert grippingzthrus't inwardly upon .the bar, and `v,means vfor :applying pressure surrounding said ruibbery ring and ,operable Vcentripetally in the chamber `to ,applyV an .inwardly directed forcible deforming -pressurezto `the ring, thereby to-,cause the ring=tof-exerticen tripetal thrust .to grip directly and iholdthe aber against longitudinall sliding orother displacement in thegripper; said `ring beingcomposedfcf 'a matrix i of -.elastically deformable Aplastic material Ahaving v embedded Atherein a, multiplicity of small, hard `metal shot giving stability sto the-masszand .improvingfthe gripping action thereof.

VI'HOMASQESLAIR HAWKES REFERENCES cir-Tian The following references .are of :record 'the Afi1cof lthis gpatent:

UNITED `'STATES PATENTS 

